Biomedical subjects
Publications and source records attributed to J Perry.
Inhalation of nitrous oxide, which inactivates vitamin B12, is followed by a rise in the plasma folate level. The concentration of plasma folate remains elevated throughout the period of exposure to nitrous oxide. Returning the rats to the air is followed by a fall to pre-exposure plasma folate levels within 24 h.
Only two (2.5%) of 80 outpatients with histologically proven ulcerative colitis had folate deficiency associated with anaemia or macrocytosis. Mean folate absorption, measured using micrograms/kg body weight of a tritium-labelled physiological folate derivative, 5-methyltetrahydroteroylglutamic acid, in six newly diagnosed patients was 76.7% (normal greater than 95%) but fell to 69.4% after three months' treatment with sulphasalazine. Mean difference in individual patients was 7.5% +/- 5.2% (SD) (p less than 0.02). Mean folate absorption in four patients with megaloblastic anaemia or macrocytosis which developed during treatment with sulphasalazine was 66.3%. This rose to 82.4% after the drug was stopped. Mean difference in individual patients was 16.6 +/- 6.6% (SD) (p less than 0.001). All patients who developed anaemia or macrocytosis with sulphasalazine had additional reasons for folate deficiency. These included coeliac disease, severe nutritional deficiencies, and haemolysis. It was concluded that sulphasalazine impairs folate absorption but this only becomes significant if other reasons for folate deficiency are also present.
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This article reviews the history of attempts to define in quantitative terms the relationship between a processed electromyographic signal and the corresponding force produced by skeletal muscle. Numerous reports have indicated a linear relationship between isometric force and rectified, integrated EMG. These reports, the nature of their experiments, and the disagreements among them are reviewed. Particular attention is given to the effects of the signal processing in the final results, including type and location of electrodes, amplification, signal isolation, etc. The effect of joint position and level of muscular effort in the isometric case are discussed. Various proposed mathematical models of the force-EMG relationship are presented and analyzed. The concluding section of the paper summarizes the current areas of agreement and disagreement and comments on the feasibility of obtaining force-EMG relation in the presence of movement.
Evaluation of rocker shoes as a walking aid for multiple sclerosis patients included a mechanical analysis of the shoes, establishment of clinical criteria for appropriate patient selection, and laboratory gait measurements of patients with and without rocker shoes. Patient fitting demonstrated that the most significant measurement, the roll point, must be about 2cm proximal to the 1st metatarsal head. A snug fit as well as the addition of a heel strap was required to hold the shoe on the foot so its mechanical assistance was consistent. Rocker shoes were effective only in patients who still retained the ability to walk independently; retention of adequate hip and calf strength proved critical. Basic gait deficit was plantar flexion less than 15 degree while standing, leading to knee hypertension and forward trunk leaning, inadequate knee flexion and toe drag in swing, general awkwardness and fatigue. Gait improvement with the rocker shoes varied with clinical classification. Normal velocity and stride characteristic in rocker shoes were accompanied by a marked decrease in net energy cost. A mean saving of 150% of normal energy was gained with rocker shoes.
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Nitrous oxide (N2O) inactivates the B12 coenzyme involved in methionine synthesis and interrupts formation of the folate coenzyme (folate polyglutamate). Normal synthesis of folate polyglutamate is restored in the N2O-treated rat when folate carrying a single carbon unit is supplied at the formate level of oxidation. The activity of the enzyme, formyl synthetase, which links formate to tetrahydrofolate, is increased after exposure to nitrous oxide. Formate is normally derived from the oxidation of methyl groups, methionine being an important source. It is suggested that failure of methionine synthesis leads to a paucity of formate and in turn to inadequate formylation of tetrahydrofolate. Formyltetrahydrofolate is the required substrate for the synthesis of folate polyglutamate, and impairment of this step in turn compromises general folate metabolism.
[2-14C]Tetrahydropteroylglutamic acid and 5-[G-3H]methyltetrahydropteroylglutamic acid were given intraperitoneally to fruit bats. Folate polyglutamates were formed in the liver from both substrates in different amounts and at different rates. The methylfolate pool appeared to remain separate from the tetrahydrofolate pool. More polyglutamate was formed from tetrahydropteroylglutamic acid than from 5-methyltetrahydropteroylglutamic acid. There was a fall in the folate content of the liver in the vitamin B-12-deficient bat and a more rapid incorporation of folates into polyglutamates but thereafter a more rapid loss of the labelled folate from liver.
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Rats exposed to N20 show a decrease in liver folate to about 25% of the initial value after 10 days. There is a transient increase in the amount of 5-methylterrahydropteroylpolyglutamate in the first 24 h, but thereafter the content decreases. The level of 5-methyltetrahydropterolymonoglutamate declines without any transitory increase. The transient accumulation of 5-methyltetrahydropteroylpolyglutamate is due to failure of methionine synthetase. Thereafter the decrease in the amount of methylfolate makes it improbable that trapping of methylfolate is the explanation for failure of folate metabolism in vitamin B12 deficiency.
These experiments characterized behaviorally two strains of rat that have been selectively bred for blood pressure differences. Avoidance performances of the spontaneously hypertensive rat (SHR) and normotensive rat (WKYN) were examined under two conditions: a discrete-trial two-way shuttle box avoidance procedure and a discrete-trial lever-press avoidance procedure. The WKYN strain reached a higher level of acquisition in the two-way shuttle box task than the SHR strain, but this difference was confounded by an initial difference in pretest avoidance rate. In contrast, the SHR strain was superior in the lever-press avoidance procedure under all conditions employed. These data are interpreted as being consistent with a hypothesis offered by Satinder that strains selectively bred for some behavioral feature may also differ in central arousal which will interact with task difficulty to determine performance differences. The data clearly indicate that the selective breeding for high and low blood pressure has simultaneously influenced the behavioral properties of these two strains.
The energetics of walking with orthoses and wheelchair propulsion at free velocity were tested in 10 adults with low-level spinal cord injuries. Eight were subjects who customarily used wheelchairs as their primary mode of locomotion; the other two used orthoses and had discontinued use of their wheelchairs. All required bilateral knee-ankle-foot orthoses to walk. A third habitual walker also was tested during walking only. Patients walked or propelled their wheelchairs around a 60.5-meter outdoor cement track. Heart rate, respiratory rate, and step frequency were recorded and transmitted by radiotelemetry. Expired air was collected for gas analysis in a polyethylene bag during the activity after a three-minute warm-up. During wheelchair propulsion all subjects demonstrated physiological responses within normal limits. Walking was significantly more difficult to perform than wheelchair propulsion (p < .005). Subjects who customarily used orthoses walked at a mean velocity of 59 +/- 5 m/min; those who primarily used wheelchairs had a mean walking velocity of 22 +/- 13 m/min. Oxygen uptake per minute was similar for both groups. These data suggest that the wheelchair will be the primary mode of locomotion for persons with spinal cord injury who need two knee-ankle-foot orthoses to walk, unless they are willing to work under anaerobic conditions and can walk at a velocity of 54 m/min or better.
Folate analogues were added to human bone marrow cells to determine their effect on deoxyuridine utilization in the deoxyuridine suppression test. Formyltetrahydrofolates fully corrected the impairment of dU utilization in pernicious anaemia marrows but tetrahydrofolate was relatively ineffective. All these analogues were effective in megaloblastic marrows from folate deficient patients. Formyltetrahydrofolates also enhanced dU utilization by normal human marrows whereas methyltetrahydrofolate reduced its use. In terms of the methylfolate trap hypothesis, the expectation that cobalamin-deficient marrows would be able to use tetrahydrofolate normally was not realized.
Exposure of rats to a 50% N2O/oxygen mixture led to a rapid loss of methionine synthase activity in both liver and brain. This enzyme has vitamin B12 as a cofactor. There was impaired conversion of deoxyuridine to deoxythymidine by bone marrow cells and this defect followed loss of methionine synthase activity. There was no homocystinuria. Withdrawal of N2O was followed by a relatively slow recovery of methionine synthase activity over four days. The inactivation of vitamin B12 by N2O promises to be a valuable tool in the study of vitamin B12 metabolism.
Preoperative and postoperative dynamic gait electromyography (EMG) weas performed on 15 patients 8 to 13 year of age with Duchenne's muscular dystrophy who underwent Achilles tendon lengthening and posterior tibial tendon transfer anteriorly through the interosseous ligament for correction of equinus and equinovarus foot deformities. The muscles tested preoperatively (anterior tibial, soleus, gastrocnemius, posterior tibial, peroneal longus, and peroneal brevis) showed phase changes. It is believed that patients with weakened leg muscles fire multiple muscle groups out of phase in an attempt to overcome the action of the stronger muscles, thus stabilizing the limb for ambulation. Postoperative EMGs, performed with the patients walking in long leg braces after the deformity had been corrected, showed little activity in the muscles tested. As the patients became dependent on the brace, the need for the muscles to be active out of phase was eliminated. The transferred posterior tibial muscle appeared to be active both clinically and electromyographically.
The effectiveness of the pes anserinus transfer, proposed by Slocum and Larson to control anteromedial rotatory instability of the knee, depends on the pes anserinus muscles contracting at times when the instability threatens the patient's function. To examine the activity of the transferred pes anserinus muscles, quantitated dynamic electromyography, isometric testing of muscle strength, and gait-analysis techniques were employed. Seven normal subjects and nine patients who had undergone pes anserinus transfer for anteromedial rotatory instability were tested. In contrast to the normal subjects, who demonstrated pes anserinus muscle activity primarily during swing phase, the patients displayed conspicuous activity of the semitendinosus, gracilis, and sartorius tendons during stance phase. Quantitated electromyography indicated that the pes anserinus muscles worked harder in the patients than in the normal subjects, and more effort was required from the muscles of patients with poor results than from those of patients with good results. All of the patients also demonstrated reduction of single-limb support time, as well as a shorter stride length and reduced gait velocity. We concluded that the pes anserinus transfer is kinetically sound. Since instability of the knee is a functional defect that is present during stance, the finding of marked activity of the pes anserinus muscles during stance phase in the patients but not in the normal subjects suggests that these muscles were being used to control the instability.
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